Magnetic shunt

ABSTRACT

A transformer having an improved magnetic shunt is disclosed. The transformer has a magnetic core which comprises at least a pair of legs defining walls of a window into which the assembled shunt is placed. The shunt comprises a plurality of laminations and includes at least a group of rectangular laminations having a pair of parallel, elongate edges with projections and cutout sections respectively disposed in that pair of edges. The laminations of the group are dimensioned so that the parallel elongate edges simultaneously abut both legs of core window. The laminations are assembled in a stacked relation. The laminations in the group may be oriented so that when the shunt is disposed in the core window, the similar edges of some of those laminations will abut one of the core legs and the similar edges of the remainder of the laminations in the group will abut the other of the core legs.

United States Patent [15] 3,693,127 Smith 51 Sept. 19, 1972 [$4] MAGNETIC SHUNT [72] inventor: Harold J. Smith, Fort Wayne, Ind. [57] ABSTRACT II u A transformer having an improved magnetic shunt is [73] Assume Ge Compmy disclosed. The transformer has a magnetic core which [22] Filed: Jan. 28, 1972 comprises at least a pair of legs defining walls of a [211 App] No 221 732 window into which the assembled shunt is placed.

The shunt comprises a plurality of laminations and includes at least a group of rectangular laminations hav- [52] US. Cl "SM/1263:2413; ing a pair of parallel elongate edges with projections int. Cl. 1 and cutout Sections respectivey disposed in that p [58] Field of Search ..336/ 155, 160, 165, 178 f edges The laminations f the group are dimensioned so that the parallel elongate edges simultane- Rderences Cited ously abut both legs of core window.

UNITED STATES PATENTS The laminations are assembled in a stacked relation. The laminations in the group may be oriented so that 2*;3; g fi et a] when the shunt is disposed in the core window, the x similar edges of some of those laminations will abut 25:8; 336/178 one of the core legs and the similar edges of the Primary Examiner-Thomas J. Kozma Attorney-John M. Stoudt et a].

remainder of the laminations in the group will abut the other of the core legs.

5 Claims, 7 Drawing Figures MAGNETIC SHUNT BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to transformers and more particularly to magnetic shunts for use in such transformers.

2. Description of the Prior Art Transformers, such as voltage stabilizing transformers, which can incorporate preferred forms of this invention, are well known in the prior art. Such atransformer has a magnetic core which serves as a closed magnetic circuit. E and I-shaped laminations, wellknown in the art, are interleaved to form the aforementioned core so as to define a pair of windows therein. A center core leg and a pair of outer core legs are thus formed in the core which define walls of those core windows. The shunt used in such a known transformer comprises a plurality of basically rectangular, magnetic laminations assembled in a staggered group arrangement and disposed in one of the core windows.

The laminations must be dimensionally narrower than the width of the window within which they are inserted to produce a staggered group arrangement yielding a predetermined air gap. In such a staggered group arrangement the laminations in each group are similarly oriented in a stacked relationship while adjacent groups of laminations are staggered with respect to each other so that each staggered group abuts one or the other but not both of the magnetic core legs defining the walls of that window in which the laminations are disposed.

In viewing this arrangement of groups with respect to one of the core legs, one group is juxtaposed with respect thereto while the immediately adjacent group is offset from that leg. The offset group cooperates with that leg to define a predetermined air gap between the shunt and the magnetic core while the juxtaposed group bridges the adjacent gap by providing an essentially low reluctance path for magnetic flux to follow. Flux entering the juxtaposed group under low load conditions will eventually pass to an adjacent group which is juxtaposed with respect to the leg toward which the flux is moving so that the flux crossing the window can travel through the shunt without crossing the large air gap between the core and the shunt. Such an arrangement does not provide positive location of the shunt with respect to the transformer core. Operation of the transformer, with passage of flux through the shunt, tends to bias all the laminations toward one or the other of the legs and thus out of their staggered arrangement.

The prior art therefore suggest the use of gap spacers disposed in some or all of the spaces between the magnetic core leg and offset sections of the shunt to prevent lamination movement and thereby to maintain precisely spaced air gaps.

ln this prior art transformer, flux passing across the transformer window would pass through the shunt under low load conditions from a first core leg into a juxtaposed section of the shunt. Subsequently, itwould have to cross a plurality of laminations and their associated boundaries to an adjacent shunt group which was juxtaposed with respect to the second core leg defining the opposite wall of that window so that the flux might pass across the core window through the shunt without crossing an air gap. Technically, a

lamination boundary is also an air gap, but the reluctance to passage of flux thereacross is much less than the reluctance provided by the much larger air gap which exists between the shunt and the core. It is in the context of this larger gap, which the term air gap is used here. The requirement that the flux cross a plurality of lamination boundaries necessitates that the flux have a higher magnetomotive force (mmf) than would be necessary if no such boundaries had to be crossed. Under high load conditions, some of the flux would pass directly from one leg to the other through the shunt and associated air gap without crossing adjacent laminations within the shunt.

The magnetic shunts of such prior art transformers are thus characterized by certain drawbacks including the need for extrinsic spacers to provide for positive location of the laminations with respect to the core and thereby maintain a precisely defined air gap, and the need for flux to cross a plurality of lamination boundaries in passing across the core window.

This invention overcomes these problems in providing a transformer with an improved magnetic shunt.

An object of this invention is to provide a transformer having an improved magnetic shunt which is positively located with respect to the transformer core so as to maintain a predetermined air gap between the shunt and the core without the need for gap spacers.

Another object of this invention is to provide a transformer having an improved shunt wherein a reduced mmf is required to pass flux from one leg to the other across the transformer core window at less than high loads because the flux need not cross an air gap between the shunt and the core leg or even a plurality of lamination boundaries in traversing the core window, but need only pass through a single lamination which abuts both legs of that window.

A further object of this invention is to provide a transformer having such an improved magnetic shunt wherein the configuration of the individual shunt laminations provides for minimum wastage of materials in the formation of those laminations.

SUMMARY OF THE INVENTION In carrying out the objects of this invention, a transformer of a type well known in the art is provided with an improved magnetic shunt arrangement. The improved shunt, comprising a plurality of laminations in a stacked relationship, is interposed in a core window of the transformers core with each of the laminations in abutting contact with both of the core legs defining the walls of that window so that the laminations are positively located with respect to the core without the need for spacers.

At least a group of the laminations are substantially rectangular planar members having substantially parallel, but distinctly configured, first and second elongate edges which cooperate with the abutting walls of the window to define a predetermined air gap. These edge configurations are complementary to each other. Thus, the laminations of the group may be formed from a strip of metal with minimal wastage of material because the same cutting action on the strip will define the complementary edges of two adjacent laminations being cut from that strip. The laminations of the group may be oriented in opposite directions whereby the first edge of some of these laminations will abut one leg of the window while all of the remaining laminations of the group will be oriented so that their first edge abuts the opposite leg of the same window. The shape of the individual laminations and the orientation of laminations in the group provide flux paths which permit flux to pass directly through the shunt from one leg to the other either directly without crossing a boundary between adjacent laminations or by merely crossing a single such boundary.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a voltage stabilizing transformer incorporating a preferred embodiment of this invention.

FIG. 2 is a perspective view of a portion of the shunt in FIG. 1, illustrating the arrangement and structure of the laminations therewithin.

FIG. 3 is a plan view of a strip of magnetic material from which a lamination has been excised.

FIG. 4 is a front view of the transformer core of FIG. 1 showing the relative orientation of the shunt with respect to the center and outer legs of the magnetic core.

FIGS. 5, 6 and 7 are enlarged views of sections of magnetic shunts with directional lines indicating the course of flux paths therethrough. FIG. 5 shows alternate flux paths in the shunt illustrated in FIG. 4. FIG. 6 is a plan view of the shunt in FIG. 5. FIG. 7 shows flux paths in prior art shunts under low and high load conditions.

DESCRIPTION OF A PREFERRED EMBODIMENT A voltage stabilizing transformer incorporating a preferred embodiment of this invention is shown in FIG. 1. The transformer comprises a magnetic core 12 formed of suitable magnetic material. Core 12 is formed of a stack of relatively thin E and I-shaped laminations alternately stacked as is well known in the art, to provide an interleaved core structure.

The magnetic core 12 includes a center winding leg 13 and outer legs 14 and 15 which cooperate to define walls of core windows having dimensional widths X and Y as seen in FIG. 4 adapted to receive coil assemblies 16 and 17. Coil assembly 16 comprises a primary winding and coil assembly 17 comprises one or more secondary windings. All of the windings are insulated from the magnetic core 12 by suitable insulation indicated at 20 and 21.

Magnetic shunts 22 and 23 as seen in FIG. 4 are inserted in their respective core windows between the coil assemblies 16 and 17. While it is contemplated that the shunt of this invention can be employed with a voltage stabilizing transformer having a center leg and two outer legs defining two core windows, it will be apparent that the shunt could be employed if desired, with a transformer having only two legs and a single window therebetween.

The following description is limited, for convenience, to a single shunt 22 in its respective window of width X. The magnetic shunt comprises a plurality of laminations, as shown in FIG. 2, each lamination being substantially rectangular with a pair of substantially parallel but distinctly configured elongate edges 24 and 25. Edge 24 is characterized by a cutout section disposed intermediate the ends thereof between a pair of spaced segments 24b. The cutout section is rectangular in nature, being defined by a pair of transverse parallel edges 24a which are connected by a longitudinal edge 24a perpendicular thereto. Edge 25 is characterized by a projection, shaped complementary to the cutout section, disposed intermediate the ends thereof between a pair of spaced segments 25b. Thus, the projection is dimensionally similar to the cutout section and is aligned therewith. In this embodiment, the projection would also be rectangular in nature, with a pair of transverse parallel edges 25a connected by a longitudinal edge 25a perpendicular thereto. While a rectangular shaped projection and cutout section are shown, the invention is not limited to that shape or even to the same shape for both the projection and cutout section. However, savings of lamination material can be had if the projection and cutout section have complementary shapes.

An advantage of the lamination configuration of this embodiment resides in the minimal wastage of material because the elongate edges 24, 25 are configured to have complementary cutout sections and projections, respectively, and because the laminations are serially formed from a strip of material. FIG. 3 illustrates a strip of magnetic material S from which a lamination Q has just been formed. Note that since the cutout section and projection are dimensionally similar and substantially aligned, the profile of edge 24 complements that of edge 25. Thus, in the formation of lamination Q from strip S, edge 24 of that lamination and edge 25 of the subsequent lamination to be formed, R, are formed with the same cutting action along the same cutting line. Since this need be the only cutting action required the repetition of it at predetermined intervals corresponding to the distance G between edges 24, 25 of a single lamination, along a strip of magnetic material having a transverse width M equal to the length of the laminations will produce the desired laminations with no significant wastage of material in the cutting process.

The overall width Z of the individual laminations (FIG. 2) is substantially equal to the dimension X defining the width of the core windows. Therefore, when the shunt 22 is inserted into its respective window, (FIG. 4) each lamination, at its edge portions 24b, 25a simultaneously abuts both legs 13 and 14 of that window at 13a and 14a whereby each lamination positively locates itself with respect to the transformer core without the use of auxiliary devices such as gap spacers. Moreover, the desired predetermined air gap is accurately determined by the configuration of the elongate edges of the lamination themselves, in cooperation with the abutting core legs, so as to comprise an area including the cutout section and the areas to either side of the projection of the lamination. This lamination configuration and its orientation with respect to the adjacent core legs is structurally advantageous when viewed with respect to the prior art because of the elimination of the need for gap spacers and because of the consequent ease of assembly of the positive, self-locating laminations of the shunt in the core window of the transformer.

As seen in FIG. 1, and more particularly in FIGS. 2 and 4, and as pointed out above, the laminations comprising the shunt are assembled in a stacked relationship with respect to each other and in an abutting relationship with respect to the transformer core legs. Additionally, it is desirable that the laminations be particularly oppositely oriented with respect to each other as well as with respect to the transformer legs 13 and 14 so that adjacent laminations are disposed with their similar edges assuming opposite orientations. Thus, each alternate lamination of shunt 22 is oriented so that the first edge, at edge portion 24b, abuts a wall portion 14a of leg 14. Each of the remaining interleaved laminations in shunt 22 abuts a wall portion 13a of leg 13 with edge portion 24b.

One effect produced by this orientation is to reduce, below prior art requirements, the mmf required to drive flux through the shunt. This can be more clearly understood with reference to FIGS. 5 and 6. Flux, passing across the window from one leg to the opposite leg, at light transformer loads, need only pass through a single lamination, as illustrated by the flux line C, without need to cross an air gap or to cross a lamination boundary between adjacent laminations. If the load on the transformer is greater, part of the flux might have to pass to adjacent laminations. However, that flux need cross only a single boundary between adjacent laminations, as illustrated by the flux line D, to find an additional flux path from one leg to the other, while it continuously travels through the shunt without the need to cross an air gap between the core and shunt. Flux line E shows a flux path followed under a relatively high load wherein part of the flux moves through the core window passing directly across the predetermined air gap in the process.

The prior art (see FIG. 7) utilized shunt arrangements employing staggered groups of laminations to provide defined, predetermined air gaps. As the path of flux line B indicates, under lower transformer loads it was necessary for some of the flux passing through the shunt to cross several lamination boundaries of several adjacent laminations in order to find a flux path through the shunt without being required to cross an air gap. The crossing of each lamination boundary increases the mmf required. Thus, the necessity for flux to cross a plurality of such boundaries meant that a higher mmf was required to drive the flux through such prior art shunts than is required by the shunt of the present invention. The flux path illustrated by flux line A is similar to that of flux line E in that it represents flux movement across an air gap under a high load.

It is emphasized that modifying prior art shunts by merely staggering the adjacent laminations so that two adjacent laminations would provide a shunt path across the core window would not achieve the same result, i.e., a reduction in the required mmf to the level achieved by the shunt of this invention. Each individual lamination of this invention, in addition to being positively self-locating with respect to the core and itself defining an air gap with respect to the core, provides a direct flux path so that there is no need for flux passing across the core window to cross any boundaries between adjacent laminations. However, in the abovementioned mentioned modification of prior art shunts, there would always be the need to cross at least one lamination boundary and thus require a higher mmf. Moreover, such a modification would not provide a positively, self-locating lamination structure.

Alternative arrangements of the laminations of the present invention are contemplated which may be advantageous to achieve specific purposes. If desired, the laminations of the present invention could be arranged in groups to form a shunt assembly wherein the similar elongate edges of the laminations within each group are similarly oriented with respect to each other but those edges are oppositely oriented with respect to the edges of the laminations of adjacent groups, in a similar fashion to that of the adjacent laminations of the preferred embodiment. That is to say that the edge portions 24b of the similarly oriented laminations in one group disposed in a core window abut one leg 13 of the core defining that window while the edge portions 24b of the laminations in an immediately adjacent group abut the opposite core leg 14 of that window. In such an arrangement, each group may comprise two or more similarly oriented laminations. As a modification of this embodiment, the shunt could comprise a single group of similarly oriented laminations.

Additionally, the laminations of the present invention could be assembled into a shunt arrangement where only some of the laminations were of the type contemplated in the present invention. The remainder of the laminations, to be used in the shunt arrangement might be of some other shape, such as ordinary rectangular laminations. These other laminations would be interposed among the laminations of the present invention. Moreover, these other laminations might be dimensioned to have an overall width 2 equal to the width of a transformer core window so that the straight, elongate edges of such laminations will be in abutting contact with the window walls such as at 13, 14 when the shunt arrangement is disposed within the transformer window.

While the above contemplated variations of the preferred embodiment do provide an improvement over shunt arrangements of the prior art, they do not achieve all of the improved results to the extent achieved by the preferred embodiment.

The above description of a preferred embodiment shows that the shunt of this invention provides an improved fiux path requiring a lesser mmf and at the same time is simpler to assemble than prior art shunts because the disclosed shunt comprises positively selflocating laminations which do not require auxiliary parts such as gap spacers.

While l have shown and described various embodiments of the invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention. It is therefore intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of my invention.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A transformer comprising a magnetic core defining a closed magnetic circuit, said core further comprising a core window having walls defined by first and second core legs;

a first coil assembly mounted on said first leg and disposed within said core window, said first coil assembly including a primary winding; a second coil assembly mounted on said first leg spaced from said first coil assembly and disposed within said core window, said second coil assembly including at least one secondary winding;

a magnetic shunt, comprising a plurality of laminations in a stacked relationship, disposed within said window between said first and second coil assemblies;

at least a group of said laminations each comprising a substantially rectangular planar member with first and second substantially parallel, elongate edges;

each of said first edges including a cutout section intermediate the ends thereof, each of said second edges including a projection intermediate the ends thereof, said projection aligned with and dimensionally similar to said cutout section;

a portion of each of said first edges abutting one of said core legs, and a portion of each of said second edges abutting the other of said core legs, thereby to positively locate said laminations with respect to said magnetic core.

2. The transformer of claim 1 wherein at least some of the laminations of said group are oriented so that said first edge thereof abuts said first core leg and the remaining laminations of said group are oriented so that said first edge thereof abuts said second core leg.

3. A transformer comprising a magnetic core defining a closed magnetic circuit, said core further comprising a core ,window having walls defined by first and second core legs;

a first coil assembly mounted on said first leg and disposed within said core window, said first coil assembly including a primary winding; a second coil assembly mounted on said first leg spaced from said first coil assembly and disposed within said core window, said second coil assembly including at least one secondary winding;

a magnetic shunt, comprising a plurality of laminations in a stacked relationship, disposed within said window between said first and second coil assemblies;

each lamination comprising a substantially rectangular planar member with first and second substantially parallel, elongate edges;

each of said first edges including a cutout section intermediate the ends thereof, each of said second edges including a projection intermediate the ends thereof, said projection aligned with and dimensionally similar to said cutout section;

a portion of each of said first edges abutting one of said core legs, and a portion of each of said second edges abutting the other of said core legs, thereby to positively locate said laminations with respect to said magnetic core;

alternate laminations oriented so that said first edge thereof abuts said first core leg while said remaining laminations are oriented so that said first edge thereof abuts said second core leg.

4. The transformer of claim 3 wherein said abutting portion of each of said first edges comprises a pair of spaced segments, one of said segments being disposed on one side of said cutout section and the other of said segments being disposed on the other side of said cutout section;

said abutting portion of each of said second edges comprises a single segment on said projection thereof.

5. The transformer of claim 3 wherein said cutout section and said projection of each lamination each has a rectangular shape. 

1. A transformer comprising a magnetic core defining a closed magnetic circuit, said core further comprising a core window having walls defined by first and second core legs; a first coil assembly mounted on said first leg and disposed within said core window, said first coil assembly including a primary winding; a second coil assembly mounted on said first leg spaced from said first coil assembly and disposed within said core window, said second coil assembly including at least one secondary winding; a magnetic shunt, comprising a plurality of laminations in a stacked relationship, disposed within said window between said first and second coil assemblies; at least a group of said laminations each comprising a substantially rectangular planar member with first and second substantially parallel, elongate edges; each of said first edges including a cutout section intermediate the ends thereof, each of said second edges including a projection intermediate the ends thereof, said projection aligned with and dimensionally similar to said cutout section; a portion of each of said first edges abutting one of said core legs, and a portion of each of said second edges abutting the other of said core legs, thereby to positively locate said laminations with respect to said magnetic core.
 2. The transformer of claim 1 wherein at least some of the laminations of said group are oriented so that said first edge thereof abuts said first core leg and the remaining laminations of said group are oriented so that said first edge thereof abuts said second core leg.
 3. A transformer comprising a magnetic core defining a closed magnetic circuit, said core further comprising a core window having walls defined by first and second core legs; a first coil assembly mounted on said first leg and disposed within said core window, said first coil assembly including a primary winding; a second coil assembly mounted on said first leg spaced from said first coil assembly and disposed within said core window, said second coil assembly including at least one secondary winding; a magnetic shunt, comprising a plurality of laminations in a stacked relationship, disposed within said window between said first and second coil assemblies; each lamination comprising a substantially rectangular planar member with first and second substantially parallel, elongate edges; each of said first edges including a cutout section intermediate the ends thereof, each of said second edges including a projection intermediate the ends thereof, said projection aligned with and dimensionally similar to said cutout section; a portion of each of said first edges abutting one of said core legs, and a portion of each of said second edges abutting the other of said core legs, thereby to positively locate said laminations with respect to said magnetic core; alternate laminations oriented so that said first edge thereof abuts said first core leg while said remaining laminations are oriented so that said first edge thereof abuts said second core leg.
 4. The transformer of claim 3 wherein said abutting portion of each of said first edges comprises a pair of spaced segments, one of said segments being disposed on one side of said cutout section and the other of said segments being disposed on the other side of said cutout section; said abutting portion of each of said second edges comprises a single segment on said projection thereof.
 5. The transformer of claim 3 wherein said cutout section and said projection of each lamination each has a rectangular shape. 